sailboat vibration prop shaft

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How to Diagnose and Fix Inboard Shaft Vibration

• By Capt. Vincent Daniello
• Updated: May 5, 2017

You know you never hit bottom, but suddenly hatch hinges clatter while underway, and a tingle starts in your feet and travels all the way through your spine. Jeff Fay, owner of Fay’s Boat Yard on New Hampshire’s Lake Winnipesaukee explains how to track down inboard engine vibrations so they don’t rattle your soul.

First, don’t overlook the prop. A floating four-by-four can knock a blade out of pitch without visible signs. Check the shaft too. “If the tip of a propeller blade is bent over, there is a good chance the shaft is bent,” Fay says. Place a dial indicator at the taper and rotate the shaft, looking for no more than two-thousandths of wobble. Check long shafts in the middle too for no more than five-thousandths variance.

TIP: When checking the alignment of the shaft couplings it’s best that the boat be floating in the water. A shaft aligned when the boat is on the trailer may no longer be aligned when the boat is floating in the water

Struts don’t become misaligned without a hard grounding, but cutlass bearings can wear out if a wad of fishing line or a lobster trap’s warp works between the shaft and the rubber bearing. Push the shaft around — any wiggle inside the bearing might cause vibration.

Next, look inside the boat. “If something is broken, it’s usually pretty obvious,” Fay explains. Compare port to starboard engine mounts, which sometimes break or crack, and so do metal brackets that attach engines to mounts. Also look for a rotting or damaged stringer.

If all seems OK, grab a helper and head out for a second look. “Sometimes the wood inside the stringer rots. The motor seems like it’s sitting alright, but when you put it under load, the mounts start moving around,” Fay says. If lag bolts holding a mount to the stringer won’t tighten and just spin when you put a wrench to them, consult an expert for solutions.

Internal mount problems often aren’t obvious. “Motor mounts have rubber inserts that can go bad,” Fay states. “Unbolt the shaft coupling and look at it.” A damaged mount usually lowers its corner of the engine. If, say, the two coupling faces are open at the top starboard-side (2 o’clock looking at the coupling from the stern) and pinched tight at the bottom port side (8 o’clock), suspect a problem with the port forward mount.

Motor mounts adjust too. A coarse adjustment left to right ensures the engine and shaft are parallel port to starboard and the shaft is centered to the engine.

Mounts also adjust for height. Often, a threaded stud fits through the engine bracket, which sits atop a large nut. Rotating that nut lifts or lowers the engine on the mount.

A nut atop the engine bracket, and sometimes a jam nut or locking tab beneath the bracket, ensures everything stays in place once alignment is set.

Alignment Steps: Lift the coupling into its proper position and check that the two faces of the coupling are roughly aligned left to right.

Next, slip the raised ridge on one coupling face into its mating groove on the other face.

Push a feeler gauge between the coupling faces — if the gap is tight at 3 o’clock and looser at 9 o’clock, or vice versa, the engine and shaft aren’t parallel in the boat.

Check the gap between coupling faces at the top and bottom too, and either raise or lower the front or rear mounts until the two faces are exactly parallel.

When all seems aligned, rotate the coupling and check around its circumference one last time before bolting it tight.

Added Flexibility: As a last resort, Fay says, a vibration-absorbing coupling insert might smooth out an otherwise rattle-prone drivetrain. Just be sure the propeller still clears the rudder once it’s pushed aft by the insert’s thickness.

• More: Engines , How-To , inboards , Troubleshooting

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Prop Shaft Vibration - Advice please

• Thread starter changeman
• Start date 26 May 2011
• 26 May 2011

Have recently been out to our boat in France and carried out a few tests to try and pin down a vibrating prop shaft problem. It starts at about 800 revs and fades away above 1200 revs. This occurs in both forward and reverse gears. I will now head for an appropriate yard to get it fixed. However, the questions are now, 1. Am I likely to damage anything on the journey if I keep the revs below 800 on the canals or above 1200 on the rivers? I usually cruise at 1000 revs. 2. Is the vibration likely to be due to an unbalanced propellor or some other problem?  

Well-known member

Having suffered a similar problem at 1800 - 2000 revs, I don't think this is due to an imbalance. I believe it to be due to some factor that causes resonance at around the natural frequency of the shaft. For interest, what is your shaft diameter and distance between bearings? Mine started when I changed engines from a Bukh to a Yanmar. I went through a long elimination process, changing P-bracket and cutless bearing, propeller, adding an Aquadrive, checking shaft straightness, none of which had any effect. There was a small amount of shaft wear in way of the cutless bearing, which I considered to be acceptable. In the end the shaft was the only unchanged component, so I replaced that. The resonance almost disappeared, although a trace of it remains. If yours is resonance the only likely damage as a consequence of motoring is to the cutless bearing, which it might be wise to replace.  

It's a huge queston and one that doesn't allow for short snappy answers. My boat has a short shaft and a three bladed prop. Vibration becomes noticeable when the cutless bearing is on the way out. I've not tried to run it for long with a worn cutless bearing and most people think my bearings would be good for another season when I change them, but I guess I'm an old woman about potential U/W failures. Prop imbalance is a potential source. If you've a modern fin keeler, shaft whip may be an issue (that often means the shaft is too thin or bent). Shaft anodes if fitted too far from the "p" bracket can compound such problems and I've seen a few fitted dead central in my time. Shaft misalignment is another possibility. Also have a good look at your engine mountings. If they are tired, or one had "gone" this will encourage shaft vibration.  

Some other problem? I'm having a new propshaft made as the old has uneven wear at the bearing. Today whilst cleaning up the prop and generally messing about, I noticed that the prop went onto the old shaft further without the key than with. Pushed on firmly but without the nut I could detect a rocking. I carefully reduced the hight of the key a few thou' at a time 'till rocking dissapeared, the prop was now 3mm further on and presumeably truer on the shaft. I can only assume that the prop was off centre and throwing the shaft off line. As this has been like it since I bought the boat I can't really comment on vibration as a 1 cylinder yanmar in an old boat shakes a bit anyway. So I assume. Hopefully the old girl will be a bit smoother when afloat again. This may have no bearing on your prob..  

FWIW When I had a vibration I discovered that one three-blade prop had lost a whole blade. I have duo-props. Easy to check and eliminate as a possibility.  

changeman said: However, the questions are now, 1. Am I likely to damage anything on the journey if I keep the revs below 800 on the canals or above 1200 on the rivers? I usually cruise at 1000 revs. 2. Is the vibration likely to be due to an unbalanced propellor or some other problem? Click to expand...

changeman said: Have recently been out to our boat in France and carried out a few tests to try and pin down a vibrating prop shaft problem. It starts at about 800 revs and fades away above 1200 revs. This occurs in both forward and reverse gears. I will now head for an appropriate yard to get it fixed. However, the questions are now, 1. Am I likely to damage anything on the journey if I keep the revs below 800 on the canals or above 1200 on the rivers? I usually cruise at 1000 revs. 2. Is the vibration likely to be due to an unbalanced propellor or some other problem? Click to expand...

• 27 May 2011

Much good advice above, unfortunately the decision on if it is bad enough to do damage will have to be yours, but have a close look at the shaft at its worst vibration at the through hull, if there is a chance it is touching stern tubes or flexing the coupling I'd go easy on it until you can get it checked out. Firstly you can't be sure that it isn't the engine unless you have disconnected it, as engine mounts age get harder engines can have resonant frequencies, but lets assume thats not the source. I would be looking at first prop, then shaft and finally bearing alignment. Many people will suggest shaft to engine alignment (at rest) but in practice this is constantly changing (unless you have an inline thrust bearing and cv joint) and the system is designed for this to be changing with shaft flex allowing the engine to move on rubber mounts without bending or breaking parts of the drive train. The vibration is more likely (once prop and shaft have been checked out OK) to be coming from a worn bearing or a bearing which is not aligned to another bearing if you have two or more. As we supply hard bearings rather than rubber I'm a bit biased in the belief that rubber slightly worn or even new allows too much flex at the bearing in some cases and even when new it's difficult to confirm if the carrier is aligned. With a hard bearing running a fine clearance on shaft and carrier a dry assembly with shaft chocked allows an engineer to check carrier alignment as the bearing can be spun by hand in the carrier whilst on the shaft if all is true. Having said that some systems have such long and thin shafts a degree of shaft flex exists through lack of support which doesn't get better when you add thrust to the equation. I wish you luck as some of these hunts for a cause can get quite protracted.  

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Trouble with folding prop, vibration

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So I recently installed a Flexofold 2-blade prop on my S2 9.2A (a 30' foot masthead sloop). My fixed 2-blade worked smoothly, no vibration, or negligeable. A couple weeks ago I installed the Flexofold, and followed the directions to the letter--you take the old prop off, and the key, then put the new hub on as far as it can go (on a tapered shaft), mark where it sits on shaft, then put back key and hub on shaft, and push until it reaches mark. I called Flexofold, and I have to say, a knowledgeable technician spent quite a while with me on the phone, going over the various causes. He seemed reassured that I had installed the prop correctly (honestly, there is not much room for error, it is pretty straightforward), especially because I said that the vibration was not consistent, it happened more aroudn 2000 rpm, and above 2500 rpm. It wasn't consistent throughout the rpms. The technician thought this indicated that the prop was balanced, and that the problem lay in maybe the added weight of the Flexofold hub exacerbating a problem that was brewing, or not yet noticeable: for ex, the cutlass bearing, in the "strut" that supports the shart, or the stuffing box, or even the way the engine was lined up--has to be exact... My question is: what do others . recommend? Any similar experiences? Diving first to see if I can pick up on problems, like a faulty cutlass bearing (the shaft should wiggle a little in there, or perhaps handling the prop itself? Or, having the boat pulled part way, for a few hours, and have a good mechanic take a look at it? I could have screwed up the installation oc the hub and blades, but I did it so carefully I doubt it. I need to have it checked, but do others have ideas of how best to start this process? I don't want, for ex, to have to have the boat hauled more that once, which would be costly.  

I think MaineSail had a thread or blog post about vibration issues with the FOF 2-blade prop. Maybe he will see this post. We have two 3-blade FOF's with no vibration issue, but that isn't relevant to you. Mark  

Here's MS's report: https://forums.sailboatowners.com/index.php?threads/folding-prop-report.140954/ Seems your experience is not unique.  

Thanks a lot Mark, and Ron, for pointing out Mainesail's posting RE- Flexofold two-blade prop experience. Very interesting. If only I had seen this before purchasing mine, I might have avoided an expensive headache. I think I'll post an update/response to Mainesail's post.  

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Prop shaft vibration, cutless bearing costs??

• Thread starter wilf
• Start date Feb 5, 2017
• Forums for All Owners
• Ask All Sailors

Wondered if anyone can help me out with this, long post i suppose but im looking at buying an 87 oday 322, boat seems to be in really good condition, above the water and had it hauled out to check underneath, no blisters or keel joint cracks, there seemed to be a bit of play in the cutless bearing maybe 1/16", when we took it out under power the prop shaft from the motor to the stuffing box had a lot of vibation there also is debris under the stuffing box what is this ( is this debris normal ) anyhow i had a guy who is a mechanic check it out and he was all doom and gloom, this is what he told me it would need, cutless bearing replaced, possibly the pilot bearing in the motor may need replaced, most likely engine mounts need replaced and could need work on the shaft or engine aligned, said it could cost $7500 to $12500 and because of that it should be a total loss! anyone had any of this work done and could tell me what it cost? I offered $10k for the boat before i found this out and they accepted the offer, the boat was donated to their foundation, any help appreciated, will try to post a video or pics of the shaft  

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This all depends on how much work you do yourself and how much you hire out. New cutlass bearing, new motor mounts, new stuffing box (or shaft seal), and maybe new shaft will run maybe $1K. None of these are particularly difficult jobs, but they can be time consuming and will provide good learning opportunities for you and your boat. If you have not done this kind of work before, be sure to get a copy of the Profanisaurus , you'll find it helpful. The good news is if you take care of these issues now, you'll be good for the next 10 or 20 years.  

Thanks, ive been in construction most of my life and am pretty handy on most things but know nothing about engines and drives etc, problem is having the place to do it, theres a boat yard near that allows diy boat work if i knew how ling it takes, also if engine mounts need replaced doesnt that involve a crane to lift the engine up?  

Trying to figure out how to post a video on here of the shaft vibration to see if its considered really excessive, cant figure it out though  

LakeOntario270

"seemed to be a bit of play in the cutless bearing maybe 1/16" Need to replace the cutless bearing. I have not done mine even though its 20 years old because there is zero side to size movement. There is a tool that will push the bearing out. I changed my engine mounts last year and it was not hard, just needs patience. I used http://www.missionsupplyonline.com/Parts/metalastik-cushyfloat Aligning the shaft is not hard, just patience. I would replace the stuffing material first with GTU before aligning the engine. I used http://www.catalinadirect.com/index.cfm?fuseaction=product.display&product_ID=2679 . The cost should come to about thousand dollars. If you need inspiration to do the job yourself, watch WhiteSpotPirates on YouTube. https://www.youtube.com/channel/UCkYfFeySHGN4DPrOc9So7PA  

Thanks, i will look at the links, im sure i can do it myself but when you changed the mounts how did you lift the motor, with a crane/hoist  

To lift the engine I used the scissor jack from my wife's Honda Civic.  

You can use a basketball to lift the engine, shove it under the oil pan deflated and fill with a pump.won't damage the pan .  

wilf said: Thanks, i will look at the links, im sure i can do it myself but when you changed the mounts how did you lift the motor, with a crane/hoist Click to expand

Engine mounts.. pretty straightforward.. ya have to disconnect the shaft coupling but a small scissors jack to do one end at a time; the basketball is a cool idea too. That said, if the top plate of the mount is not touching the bottom plate and has 3/16 or so clearance at both ends, the mounts are still OK.. One of those things .. might look terrible but still be OK.. clean 'em up and check clearance at both ends of all four. I would discount the "pilot bearing" comment.. The shaft may be bent or the prop may have a lot of growth on it causing the vibration.. A bent shaft can be found easily by uncoupling then rotating the shaft by hand while watching/measuring the gap between the engine side coupling and the shaft coupling. If the gap wide part rotates with the shaft, shaft is bent or the coupling is shot.. First really is to try to align the engine output to the shaft while the shaft is held in the center of the stern tube, the part that the packing box hose connects to. This can and should be done with the boat in the water. If the prop is clean and has no barnacles and the shaft is straight, alignment may solve the vibration.. Good luck with it.. Ya might want to talk to another mechanic guy..  

There is a logical sequence in these repairs that may not be immediately apparent, but can make the whole job go more smoothly. 1. Get boat out of the water. 2. Loosen the stuffing box. 3. Disconnect shaft coupling from the transmission. 4. Remove coupling from shaft. 5. Remove shaft from boat. Check for wear and straightness. Replace if needed. 6. Remove and replace cutlas bearing. 7. Determine if stuffing box can be reused. Replace the hose (use hose designed for stuffing boxes). Replace if necessary. 8. Inspect engine mounts, clean and replace if necessary or if it looks like they will need replacing in the near future. Do it now to get it behind you. 9. Put everything back together. 10. With boat in water, align engine to shaft. And before you start this, buy a case of PB Blaster.  

That is a lot of money. It isn't all that hard. Get the tool to push out and replace the cutlass bearing or make your own. All thread and some pipe fitting or old bearing which is close to the size but slightly smaller that the housing. Motor mounts are not too expensive and easy to replace. The most expensive part is shaft seal parts. You may need a new shaft. A local machine shop can duplicate yours. It is a project, but if you can change a waterpump on a a modern car, and have some tools and mechanical aptitude just about anybody can do this.. There is all kinds of stuff on the the net for diy on all of this.  

Thanks guys, i thought the costs were way too high, and i am sure i can do it myself ive replaced a couple of car engines myself 20+years ago, i have a good friend that is an excellent diesel mechanic but lives 2000 miles from me i sent him the video of the shaft vibrating and he said straight away cutless bearing and possible damaged shaft, does anyone think the vibration may only be something as easy as just the cutlass bearing? , wish i could figure out how to post the video on here? And will have someone inspect the mountings more closely, the guy who told me how expensive it would be was actually a guy i got 2nd to look at it, first guy just said the cutless bearing  

wilf said: Wondered if anyone can help me out with this, long post i suppose but im looking at buying an 87 oday 322, .. I have just finished replacing my shaft, cutless brg. and packing gland on an Endeavour 35. I see some really good advice on solving your problem. Have you considered a dripless shaft seal? Mine is working very well and I did the installation-easy DIY but you will have to remove the shaft coupling. Here you can place a ratchet socket (same size or close to the diameter of the shaft) between the end of the shaft and the trans output shaft. Using 2 longer bolts through the coupling tighten and the coupling will back off. I agree with having your shaft analyzed for straightness and maybe you'll want your prop looked at also. Could be bent? Clean up those mounts and if they are ok per previous posts, apply some Ospho and paint 'em. I also used some allthread, washers and a piece of galv pipe to pull out the cutless brg. You can also press the new one back in place using same tooling. I learned a lot and saved the $120.00/hr yard rate! Click to expand

thanks Greg I seen them, they will be helpfull  

Another question to any oday 322 owners, the big square floor panel at the bottom of the entry steps to the cabin behind the small bilge access panels, does this come up or is it fixed, if its liftable whats underneath it? Also any 322 owners added an outboard to the steped transom?  

Given that the bearing tool if purchased is probably twice the price of the bearing. and changing the bearing is an afternoon if you've never done it, why not change the bearing and see what that does first, if you have to change the shaft, after, your cost of the tool went down by 50% because you've got some good use out of it already.  

Homemade tools do not always work well at removing the cutlass bearing. A hacksaw and a small cold chisel work well. After removing the shaft, insert a hacksaw blade into the bearing and cut the bearing. Be careful to not cut the strut. Once the bearing is sliced lengthwise, use the chisel to collapse the bearing and remove it. Home made tools work better pressing the new bearing in place. Use some flat iron instead of washers, the washer will sometimes deform.  

Just thought i would let you all know for comments, I went to the boatyard this morning and these are the prices they gave me Haulout $320 Rudder removel so shaft can be removed $720 RR shaft replace ( dont know what that is ? ) $870 Replace complete shaft $1500 Replace engine mounts re align motor $2200 Replace cutless bearing $500 Total cost $6110. Maybe a bit less if the shaft only needs straightened  

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Experiencing Boat Vibration At Low Speed? Here’s What It Could Be…

Most sources of boat vibration at low speeds on your boat are related to the running gear or propulsion system.

When troubleshooting the source of boat vibration, it is helpful to approach the search methodically and inspect the most common causes first.

In this article, we will start at the prop, work our way up to the engine, and look at the factors that could be causing your boat’s vibrations.

Table of Contents

What is the most common cause of boat vibration, boat vibration at low-speed due to outboard motor, boat vibration due to bent or loose shafts, inspect the cutlass bearing if your boat vibrates, damaged and loose motor mounts can cause boat vibrations at low speed, how to check your boat’s engine alignment, design flaws that cause boat vibrations, does vibration on a boat cause damage, rounding up the most common reasons for boat vibration at low speed.

There are many reasons why your small boat may be having issues. According to the University of Washington , gas levels, engine problems, and propeller errors can all cause simple issues!

By far, the most common source of vibrations at low speeds is because of the prop. And, since it is fairly easy to diagnose visually, it’s a good place to start troubleshooting.

Any broken blades will cause dramatic vibrations, but even small nicks or gouges can be enough to disrupt the push of the water, causing your boat to run rough.

Usually, the damage is caused by running aground, hitting a partially submerged log, or debris. But weaknesses can develop, and propeller damage can appear without a precursor event.

Broken propellers are usually fixed with a replacement. However, if just one blade has been bent, a propeller shop may be able to restore the proper pitch.

Badly fouled props due to barnacles and marine growth will also cause a vibrating sensation. Fouled props will also be accompanied by a lower speed than expected at a given RPM and a reduced reaction time when turning. 

A quick scrape to remove the barnacles is a quick and easy fix. Specially designed antifouling paints that are engineered to withstand the high speeds of a prop can extend the time between cleanings.

Whether your boat has an inboard engine or an outboard motor, the most common sources of boat vibrations are the same–most likely stemming from the propeller, engine, or engine alignment.

The same methodical approach to troubleshooting can be applied.

Here are the most likely sources of boat vibration at a low speed from your outboard engine…

Inspection of the propeller is even easier with an outboard. Look at the spacing between the fin of your lower unit (closest to the propeller) and the blade of the propeller itself. Turn your prop and measure the distance for each blade.

If there is any variation in that distance for any of the blades, either the propeller has sustained damage or the prop shaft has been bent.

To be completely confident there is no debris caught in the hub, remove the propeller, and grease the shaft before replacing it.

If the prop and shaft are aligned, then the engine mounting bolts should be inspected for any looseness or shifting.

Once the most common sources—and easiest to diagnose—are eliminated, then it’s time to investigate the engine as the source.

The starting point for troubleshooting, especially if only experiencing vibrations at low RPMs or at idyl, would be to check the throttle and work outward from there.

If the propeller is clean and in good shape, the next source to investigate is the shaft.

A bent shaft is usually the result of either running aground or fouling a crab trap or lobster pot line in the prop. Even a thin fishing line tangled in the prop may put enough force on the running gear to cause a minor inflection in the shaft.

If the shaft is damaged, it will require removal. And, in most cases, replacement.

Another potential source of vibration could be from the shaft struts—the running gear that holds the prop after it leaves the boat through the cutlass bearing but before the propeller.

If there is free movement where the metal strut attaches to the fiberglass hull, the shaft will wobble, and it will cause a vibration.

Less commonly seen is what is referred to as “whipping.” Whipping is a sag in the shaft that forms from a combination of low use and insufficiently supported shaft system.

This is a design flaw that would bear investigation before replacing the bent shaft.

The cutlass bearing—the point where the shaft exits the hull into the water—can also be the source of vibrations.

There are two primary types of cutlass bearings. One allows for a small but steady stream of water to run past the shaft and into the boat. The other, a dripless cutlass bearing, recirculates water over the shaft allowing for a dry bilge.

Both styles allow water to flow over the shaft. With insufficient water flow, the shaft will become excessively hot while turning due to friction.

If either type of cutlass bearing is restricted too much, the excess heat will cause damage to the bearing (and possibly the shaft).

In addition, sand can get caught in the mechanism, causing damage to the bearing or wearing a groove into the shaft.

This type of damage is frequently seen after hauling a boat out to repaint the bottom. Pressure washing, sandblasting, sanding, and even just dusty boatyards can allow contaminants to get stuck in the fragile orifice.

Inspecting the bearing before putting the boat in the water is prudent.

While damage to the cutlass bearing or the shaft inside the cutlass bearing can lead to vibrations, it is also important to note that vibrations caused by prop damage or engine alignment problems can cause excess wear on the cutlass bearing and be a symptom, not the source of the problem.

Another common source of boat vibration at low—and higher—speeds is a broken or loose motor mount. There is an incredible force on the mounts as the boat is rocked or jarred by large waves and wakes.

The motor mounts rest on strong rubber pads to absorb the shock of the boat’s motion and the engine’s motion. These can deteriorate. Or the bolts from the mount into the boat hull can become loose. The metal mounts themselves can crack. 

Even just one loose motor mount will allow the shaft to wobble enough to cause a vibration. The effect can be especially noticeable when the engine is just starting and at lower RPMs.

Once the prop and shaft are eliminated, then the engine itself becomes the possible source of vibration.

One of the most common sources of boat vibration is caused by an engine that needs alignment. The shaft must be perfectly lined up with the transmission and the damper plate of the engine.

Even a few thousandths of an inch off will put pressure on the internal workings of the transmission, place uneven pressure on cutlass bearings, and cause enough instability in the shaft to vibrate the boat.

You can check the alignment in the water by removing the four bolts that attach the shaft to the transmission. Gently slide the shaft down and back into place—pushing it snugly, and aligning the bolt holes again.

Then, use a feeler gauge—one can be purchased from an auto part or marine store—and run the three-thousandths of an inch (0.003) gauge between the two plates.

If the gap is too tight to run freely all the way around, the engine needs alignment. This is done by adjusting the motor mounts.

Other, less common, vibration sources stemming from the engine itself can be poorly aligned belt pulleys, bad injectors, loose mufflers, or other engine accessories. These cause the engine movement to exceed the amount the motor mounts can absorb.

So far, we’ve explored sources that would cause a boat to start vibrating.

If you’ve always had a vibration on your boat, it could be that the propeller is too large and doesn’t have clearance between itself and the hull. The turbulence affects the prop wash.

Or another design flaw that could cause vibration is that the shaft is too long or not properly supported. A long overhang could cause a wobble in the shaft as it starts to push, causing the vibration sensation.

Most sources of boat vibrations at low speeds can be diagnosed readily, and many are easy fixes.

However, leaving the problem unresolved can cascade into a variety of damage, from broken motor mounts to prematurely worn-out transmissions, so priority should be given to identifying and resolving the problem.

While there are several things that can cause your boat to irritatingly vibrate, here’s a quick recoup of the most likely reasons:

• Damaged propeller (inboard or outboard motors)
• Damaged propeller shaft (inboard or outboard motors)
• Cutlass bearings (inboard motors)
• Engine mounts or alignment (inboard or outboard motors)
• The engine is in need of maintenance or service (inboard or outboard motor)

Takeaway Tip: Always start with the most likely culprit, the prop !

Growing up in Florida, I’ve been surrounded by saltwater my entire life…and I love sharing my passion with others.

To learn more about why I started Saltwater Mecca, visit the ABOUT page.

Thank you for reading this article. Browse around & have some fun!

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Prevents Electrolysis

DriveSaver® provides an impervious barrier that blocks electrical currents from the water to protect your engine and transmission from damaging electrolytic corrosion.

Acts Like a "Circuit Breaker"

DriveSaver® absorbs extreme shock and torque usually caused by a hidden log, line, or rock. DriveSaver® is designed to break apart, leaving your transmission and engine intact. That's right. DriveSaver® gets destroyed, not your costly transmission and engine. That's the kind of total protection you can't afford to be without!

Installs Easily

DriveSaver® installs simply and quickly, No cutting or machining is required. And, you don't have to haul your boat out of the water. just separate the drive flanges, insert the coupling, align DriveSaver® and bolt together.

There are over 40 models of the DriveSaver ® marine breakaway coupling available for the largest marine engine transmission manufacturers in the world.  Visit the Globe Marine website to find the right DriveSaver ® for your application.

Shaft Lok provides a means to safely lock the propeller from spinning whilst sailing. This ensures noise from a spinning prop and shafting is eliminated. A spinning prop can also build up heat in the transmission and lead to unnecessary wear. Long term freewheeling will wear all drive train components unnecessarily.

While sailing SHAFT LOK locks the propeller in the most efficient position, vertical in the rudder and keel opening (if that is what you desire), for the best boat speed,quiet operation and without transmission or propeller shaft bearing wear.

A spinning propeller will cause more drag due to the propeller windmilling, generating greater drag than when stationary. Hence locking the propeller will eliminate drang and thus facilitate speed. During a manufactures comparison tests it was discovered that a standard 15 inch diameter 3 blade propeller increases the resistance of the hull by 48 pounds, the equivalent of dragging a large bucket behind the boat. Shaft Lok by design holds the propeller stationary regardless of yacht speed. All that is necessary to release the lock is to start the engine and engage the transmission. SHAFT LOK automatically unlocks.

Shaft-Lok fits to the shaft between the shaft half coupling and the gland, so it is necessary that there is enough space for the disc to rotate clear of the bottom.

The unit is engaged by pushing down on the knob directly, or via the remote cable if fitted. This is more easily done if the boat is brought head to wind for a short while or boat is slowed right down by use of reverse gear before shutting the engine off. It automatically unlocks after the engine is re-started and put into reverse gear for a moment.

Maximum cable length is 13 feet. Sometimes longer cables can be provided depending on the routing of the cable itself.

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Shaft vibration

Discussion in ' Inboards ' started by Deering , Jun 2, 2019 .

Deering Senior Member

Hi all. I’m performing sea trials on my catamaran conversion project and have noticed some shaft vibration on one shaft. I’m not sure how much of a problem I have. These are pretty long shafts, with about 11 feet between the thrust and cutless bearings. The stuffing box is about midway, but is only connected to the stern tube with heavy rubber hose, no hard connection. At the engine end the shaft is mounted to an Aquadrive, a fixed thrust bearing mounted to the hull that connects to the transmission through a pair of CV joints - engine alignment is decoupled from shaft alignment. It’s a 1.5” Aquamet 22 shaft. New. The prop is new as well. The other shaft exhibits no visible vibration. I haven’t measured the amplitude at the stuffing box (mid-length) but a rough eyeball estimate might be 1/8 of an inch at most. I don’t hear/feel significant vibration. When I rotate the shaft by hand (no problem with that) I’m measuring about .006 inches of runout, though I can physically flex the shaft a lot more than that. I have a number of trips ahead of me soon, and pulling the boat would be problematic. I can dive on it to inspect the prop but I suspect that if it has any damage it’ll be difficult to detect it underwater. It’s Alaska so diving consists of a bit more than just a mask and snorkel. So is this a crisis I must deal with immediately? Is there anything else I can do to further evaluate the problem? Any advice welcomed.  

Ad Hoc Naval Architect

Deering said: ↑ These are pretty long shafts, with about 11 feet between the thrust and cutless bearings. ....It’s a 1.5” Aquamet 22 shaft. New. Any advice welcomed. Click to expand...

gonzo Senior Member

The shaft is pretty long for the diameter. Also, an Aquadrive is not a magic solution to gross misalignment. Make sure the engine/shaft alignment is within the limits of the system.  

gonzo said: ↑ The shaft is pretty long for the diameter. Also, an Aquadrive is not a magic solution to gross misalignment. Make sure the engine/shaft alignment is within the limits of the system. Click to expand...

Ad Hoc said: ↑ If that long thin shaft of 11 feet has just 1 minor support mid way - that is way way too long for a shaft to be unsupported. Click to expand...

Deering said: ↑ It’s at the outside bounds of the recommendations given in Dave Gerr’s book on boat mechanical systems. Shaft material plays a role - this one is AQ-22. The other identical shaft is performing flawlessly (so far). I can add a fixed bearing into the system, if warranted, but not until the end of the season. Click to expand...

Ad Hoc said: ↑ Can never go wrong with more support, especially on such a long thin shaft. Maybe worth checking the balance of the prop too? Click to expand...

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Sam Smullin New Member

The max bearing spacing for a 1.5" aquamet 22 shaft at 900rpm is 7.27'. I would add a support bearing sooner rather than later, running with that much unsupported shaft could result in breaking a shaft. If your shaft RPM is above 900 the minimum bearing spacing will be reduced. sam  

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Bruntons SigmaDrive

Stops noise and vibrations..

The compact shaft coupling solution. SigmaDrive is a low maintenance, high torque, bearing free solution that stops noise and vibration. SigmaDrives can cope with a 3 degree misalignment of the shaft in any direction; 6 degrees in total and, unlike most CV shafts, the DS intermediate shaft coupling can be fitted inline or at an angle making installation much easier and faster.

Even if an engine and propeller shaft are perfectly aligned when the vessel is built, maintaining that alignment when the engine is running and the vessel moving is an impossibility. However well the boat is built, that allows noise and vibration to be generated. SigmaDrive anti-noise and vibration solutions are available for virtually every type of craft with engines up to 1300hp.

No more alignment & vibration worries

No more noise & vibration from misaligned shaft & bearings.

• Compact size, comparable to a standard shaft coupling.
• Provides perfect alignment for the propeller shaft and works perfectly in line or out.
• Easy and quick to fit, usually without slipping the vessel and without the need to modify the propeller shaft, or fit fixture plates or brackets for thrust bearings that are no longer required.
• Contains no rubber or bearings, and is manufactured from a special alloy that ensures long life with little maintenance requirement.
• A highly cost effective solution requiring little or no costly modifications to the vessel.

Why does a SigmaDrive work so well? Because SigmaDrive is a constant velocity joint which allows the propeller shaft to rotate without transmitting the engines movements and vibrations .

Other attempts at solving these solutions rely on rubber couplings or Carden units. The SigmaDrive requires none of these, is compact and easy to fit, usually without slipping the vessel or requiring modifications to the shaft line. It’ s a premium product manufactured from a special bronze alloy that is maintenance free and its internal components are hard wearing and long lived.

Would you like to discuss SigmaDrive without obligation?

If you are interested in our products, we would like to send you further information. Please fill out the form below and we will contact you immediately. Or feel free to call us at 401-847-7960

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